The present invention is generally directed to toner compositions and processes thereof, and more specifically to the surface modification of toners, including in situ toners, and overcoated toner compositions directly generated from toner compositions without resorting to the conventional pulverization and classification methods. In one embodiment, the present invention relates to the surface modification of toners by an aqueous oxidation and metal chelation thereof, thereby providing excellent flow characteristics without the use of known flow additives, like colloidal silicas, and wherein the toner flowability is excellent, such as from about 1 percent to about 20 percent cohesion as measured by the HOSOKAWA FLOW TESTER.TM.. In another embodiment, the present invention relates to the surface modification of toners by an aqueous oxidation and metal chelation thereof, followed by the coalescence, that is absorption of fluorinated resins by emulsion polymerization to control the triboelectrical properties thereof, and to enable toners without the use of known flow additives, like colloidal silicas, with excellent flow characteristics, of from about 1 percent to about 20 percent cohesion as measured by the HOSOKAWA FLOW TESTER.TM., and wherein the toner compositions treated in embodiments are comprised of a core comprised of a polymer resin and colorants, including color pigments, dyes, or mixtures thereof, and an outer coating layer comprised of a cellulose component, such as methyl cellulose, hydroxypropyl cellulose, hydroxyethylmethyl cellulose, and the like, and wherein the cellulose layer functions primarily as a protective coating for the core components, especially during the preparation thereof, and thereafter the cellulose is oxidized and metal chelated with a metallic oxidizing reagent such as cerium ammonium nitrate, chromium oxide, chromic acid, potassium permanganate and the like. The processes of the present invention in embodiments thereof are comprised of an initial dispersion step for forming a stabilized organic microdroplet suspension in an aqueous medium containing a cellulose surfactant, a hydroxyalkyl cellulose, wherein alkyl contains from 1 to about 12 carbon atoms, such as hydroxyethylmethyl cellulose, methyl cellulose or the like; followed by the free radical polymerization of the core monomers; and subsequently oxidizing and metal chelating the surface thereof with an organometallic or metallic containing reagent such as cerium ammonium nitrate, or chromium oxide and the like, and optionally thereafter coalescing or an absorbing fluorinated polymer or polymers by emulsion polymerization to control the triboelectrical properties thereof, and to enable toners with excellent flow characteristics without the use of known flow additives of from about 1 percent to about 20 percent cohesion as measured by the HOSOKAWA FLOW TESTER.TM..
In reprography, such as xerographic or ionographic technologies wherein single and two component development can be utilized, black or colored dry toners are employed. It is often very desirable that the aforementioned toners particles with excellent toner characteristics are utilized, such as excellent powder flow of from about one percent cohesion to about 20 percent cohesion, and preferably from about 3 percent cohesion to about 10 percent cohesion as measured by the HOSOKAWA POWDER TESTER.TM.. Excellent powder flow is usually necessary for the effective development and transfer of a toner image. Toner particles of from about 5 microns in diameter (average volume) size to about 20 microns in diameter can be selected, and transfer of toner from a packaged container into a machine developer housing is effected smoothly and efficiently without, or with minimal clogging or remaining aggregated toner in the packaged container. Additionally, the mixing of toner with carriers in a developer housing should also proceed in a timely and sufficiently homogeneous manner such that toner clumps are not isolated from the carrier component. Accordingly, toners with poor flowability can cause uneven toner image mass, adversely affecting triboelectric charge characteristics and hence cause poor image development, and poor image resolution. To overcome some of these problems, it is customary to blend onto the toner surfaces external additives such as colloidal silicas, tin oxide or metal stearates, such as zinc stearate and the like. These aforementioned external additives can be submicron in sizes ranging from about 5 nanometers to about 100 nanometers for colloidal silicas and tin oxide, and from about 0.1 micron to about 4 microns for the metal stearates. Furthermore, the external additives are usually dry blended onto the toner surfaces employing high shearing devices such as a Lightnin blender, and it is important that overblending or overshearing is avoided so that the toner particles are not fractured or damaged during the processing thereof. However, the use of submicron external additives onto the toner surface may have an impact on health issues, due to the ease at which these submicron particles are airborne, especially during the transfer of fresh toner into a developer housing. Furthermore, the use of external additives onto toner surfaces can cause mechanical failures or deterioration of machine performance due to the accumulation of submicron particles into other machine parts, especially after extensive use. The toners and processes of the present invention in embodiments eliminate or overcome these difficulties through the chemical modification of the toner surfaces by oxidizing and metal chelating the toner surfaces, thereby providing excellent powder flow, without the use of external blended additives, such as colloidal silicas and the like, of from about 1 percent to about 20 percent cohesion as measured by the the HOSOKAWA POWDER TESTER.TM.. The surface modifying reagents are oxidizers and metal containing reagents such as cerium ammonium nitrate and the like. The use of a non-metallic oxidizing reagent such as sodium periodate, can oxidize the toner surface and modify the triboelectric charge thereof, and it is found that poor powder flow characteristics, such as from about 25 percent to about 70 percent cohesion are obtained with such reagents as measured by the HOSOKAWA POWDER TESTER.TM.. Therefore, it is important that the reagent contain a metal species capable of chelating or complexing in addition to oxidizing.
Additionally, in color reprography, such as in full color or highlight color applications, colored toners with a wide variety of colors including black are usually employed. For two component development, it is highly desirable that the triboelectric properties of different colored toners be desirably controlled so that they all attain similar equilibrium triboelectric charging levels when utilized against a selected carrier. This is especially useful for custom colored toner packages, since colored toners with a wide variety of custom colors can be obtained by simple blending of the primary colored toners. Another important aspect for two component development is the rate of charging of the fresh toners to the equilibrium charge levels when they are added to the toner depleted development housing. A fast rate of charging of fresh toner can be important in ensuring proper image development, particularly for high speed reprographic systems. These and other advantages are enabled with the compositions and processes of the present invention in embodiments. It is known that color pigments or dyes present in the toner have a dominant effect on the toner's triboelectric charging behavior, arising primarily because these colorants are often also present at or close to the surface of the toner, and are, therefore, exposed to their environments. As a consequence, when the toner particles are admixed with carriers, the interactions of the exposed pigments of the toners with the carrier particles may drastically affect the charging behavior of the toner. Similar effects are obtained for a number of prior art encapsulated toners where the color pigment particles are not completely encapsulated within the toner shell. Thus, it is often observed that toners with identical components, except colorants, exhibit different charging behavior, even to the extent of having triboelectric charges of opposite polarity. To overcome this difficulty, it is usually necessary to utilize different charge control additives for different colorants, or to use high levels of charge control additives so as to nullify or overcome the different charging effects of different colorants, and thus minimize the dominating influence of the colorant on the charging characteristics of the toners. The toners and processes of the present invention in embodiments eliminate or minimize this difficulty through the coalescence or absorption of fluorinated resins by emulsion polymerization onto the toner surface modified by oxidation and metal chelation by a metallic reagents such as cerium ammonium nitrate and the like. As a consequence, the need to rely on different or high levels of charge control additives for different colored toners for achieving similar triboelectric charging levels is eliminated or substantially minimized, and wherein excellent flow characteristics results such as excellent powder flow of from about (throughout includes the ranges in between) 1 percent to about 20 percent cohesion as measured by the HOSOKAWA POWDER TESTER.TM.. Other advantages associated with the toner compositions obtained by the processes of the present invention include, for example, rapid triboelectric charging rates, small toner size and narrow size distribution for high resolution images, excellent color mixing properties and image color fidelity, high image projection efficiency enabling their use on transparent substrates, lower fusing temperatures, and toner nonblocking and nonagglomerating characteristics.
Furthermore, the surface modified toner compositions of the present invention can be selected for a variety of known imaging and printing processes including electrophotographic and ionographic processes.
Encapsulated toners and processes are known. For example, U.S. Pat. No. 4,626,490 discloses an encapsulated toner comprised of a core material comprised of a long chain organic compound and a higher carboxylic acid encapsulated with a thin shell material; see Example 1, column 10, line 12, wherein an external additive comprised of fine powdery SiO.sub.2 was used for image formation, and also Examples 2 through 9 employing similar external additives. The toners of the present invention, through the oxidation and metal chelation of the surface thereof, does not require external additives and are utilized as such in image formation. There is also disclosed in U.S. Pat. No. 4,797,339 an in situ toner comprising an inner layer comprised of a resin ion complex having a coloring agent and an outer layer containing a flowability imparting agent; see column 5, lines 3 to 13, wherein the flowability imparting agents in addition to the perfluoroalcohol acrylate agent, includes benzoquanamine formaldehyde resin and hydrophobic silica. Similarly, U.S. Pat. Nos. 4,789,617; 4,601,968; 4,592,990; 4,904,562; 4,465,756; 4,468,446; 4,533,616; 4,565,763 and 4,592,990 also disclose the use of external surface additives to toner surfaces prior to image formation.
Encapsulated toners displaying triboelectric charge passivation are also known. For example, U.S. Pat. No. 4,937,167, the disclosure of which is totally incorporated herein by reference, discloses an encapsulated toner comprised of a core resin, colorant and polyurea shell wherein triboelectric nullification or passivation is achieved. However, note column 17, lines 2 to 14, wherein external additives, such as AEROSILS.RTM., aluminas or silicas, are added onto the toner surface prior to image formation, and note Example 1, column 21 on line 16, wherein additives including charge control agents are blended onto the toner prior to image formation. The encapsulated toners of the present invention, through the oxidation and metal chelation of the surface followed by coalescence of fluorinated resins thereof, results in triboelectric charge control or passivation without the use of external additives, and can be utilized as such in imaging and printing apparatuses. Other prior art relating to encapsulated toners and processes thereof include U.S. Pat. Nos. 4,803,142; 4,656,111; 4,517,273; 4,543,312; 4,609,607; 4,784,930; 4,307,169; 4,617,249 and 4,702,989.
Additionally (D/90516), now U.S. Pat. No. 5,175,071, the disclosure of which is fully incorporated herein by reference, discloses an in situ toner comprised of a core resin, colorant and cellulose shell coating, and wherein passivation results, however, surface additives are also added onto the surface by blending prior to image formation.
There is a need for black or colored toners wherein excellent flow characteristics are obtained without the use of external additives. Furthermore, there is a need for colored toners wherein the triboelectric charge is not influenced by the colored pigment employed, also known as passivation, wherein the use of external additives is avoided or minimized and result in excellent toner flow characteristics. In addition to the above, there is also a need for black and colored toners that are nonblocking, of excellent image resolution, and nonsmearing.